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Applying Semantics to Service Oriented Architectures

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Applying Semantics to Service Oriented Architectures

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  1. Applying Semantics to Service Oriented Architectures Oasis Symposium 2006 The Meaning of Interoperability 9-12 May, San Francisco Presenters: Adrian Mocan Mick Kerrigan Michal Zaremba Special Thanks to: Emilia Cimpian Thomas Haselwanter Brahmananda Sapkota

  2. The Aims of this Tutorial • Introduce the aims & challenges of Semantic Web Services (SWS) - the WSMO approach • Describe how SOA can be used with Semantic Web Services – WSMX Approach • Semantic SOA enables interoperability OASIS Symposium 2006

  3. Overview • Introduction to SWS • WSMO • Introduction to SOA • WSMX • Means of Interoperability • Web Service Modeling Toolkit (WSMT) • Conclusions OASIS Symposium 2006

  4. Overview • Introduction to SWS • WSMO • Introduction to SOA • WSMX • Means of Interoperability • WSMT • Conclusions OASIS Symposium 2006

  5. Introduction to Semantic Web Services • Introduction to Semantic Web • Introduction to Web services • Semantic Web Services OASIS Symposium 2006

  6. Semantic Web and Web Services – The Vision 500 million user more than 3 billion pages WWW URI, HTML, HTTP Static OASIS Symposium 2006

  7. Semantic Web and Web Services • Serious Problems in • information finding, • information extracting, • Information representing, • information interpreting and information maintaining. Semantic Web RDF, RDF(S), OWL WWW URI, HTML, HTTP Static OASIS Symposium 2006

  8. Semantic Web and Web Services – The Vision Web Services UDDI, WSDL, SOAP Dynamic • Bringing the computer back as a device for computation Semantic Web RDF, RDF(S), OWL WWW URI, HTML, HTTP Static OASIS Symposium 2006

  9. Semantic Web and Web Services – The Vision • Bringing the Web to its full potential Intelligent Web Services Web Services UDDI, WSDL, SOAP Dynamic Semantic Web RDF, RDF(S), OWL WWW URI, HTML, HTTP Static OASIS Symposium 2006

  10. conceptual model of a domain (ontological theory) unambiguous terminology definitions commonly accepted understanding machine-readability with computational semantics Ontology Definition Formal, explicit specification of a shared conceptualization OASIS Symposium 2006

  11. Ontology Example Concept conceptual entity of the domain Attribute property of a concept Relation relationship between concepts or properties Axiom coherent description between Concepts / Properties / Relations via logical expressions name email Person studentnr. research field isA – hierarchy (taxonomy) Student Professor attends holds Lecture lecture nr. topic holds(Professor, Lecture)  Lecture.topic  Professor.researchField OASIS Symposium 2006

  12. Ontology Languages • Requirements: • ”expressivity“ • knowledge representation • ontology theory support • ”reasoning support“ • sound (unambiguous, decidable) • support of reasoners / inference engines • Semantic Web languages: • web compatibility • Existing W3C Recommendations: • XML, RDF, OWL OASIS Symposium 2006

  13. Semantic Web Language Layer Cake OASIS Symposium 2006

  14. Web Services • Web Services [Stencil Group] • loosely coupled, reusable components • encapsulate discrete functionality • distributed • programmatically accessible over standard internet protocols • add new level of functionality on top of the current web OASIS Symposium 2006

  15. Using Web Services OASIS Symposium 2006

  16. Using Web Services Syntax Only OASIS Symposium 2006

  17. Lack of SWS standards • Current technology does not allow realization of any of the parts of the Web Service usage process: • Only syntactical standards available • Lack of fully developed semantic markup languages • Lack of semantically marked up content and services • Lack of semantically enhanced repositories • Lack of frameworks that facilitate discovery, composition and execution • Lack of tools and platforms that allow to semantically enrich current Web content OASIS Symposium 2006

  18. Semantic Web Services • Define exhaustive description frameworks for describing Web Services and related aspects (Web Service Description Ontologies) • Support ontologies as underlying data model to allow machine supported data interpretation (Semantic Web aspect) • Define semantically driven technologies for automation of the Web Service usage process (Web Service aspect) OASIS Symposium 2006

  19. Semantic Web Services (2) Usage Process: • Publication: Make available the description of the capabilities of a service • Discovery: Locate different services suitable for a given task • Selection: Choose the most appropriate services among the available ones • Composition: Combine services to achieve a goal • Mediation: Solve mismatches (in data or process) among the combined services • Execution: Invoke services following programmatic conventions OASIS Symposium 2006

  20. Semantic Web Services (3) Usage Process – execution support • Monitoring: Control the execution process • Compensation: Provide transactional support and undo or mitigate unwanted effects • Replacement: Facilitate the substitution of services by equivalent ones • Auditing: Verify that service execution occurred in the expected way OASIS Symposium 2006

  21. Summary Semantic Web Services = Semantic Web Technology + Web Service Technology OASIS Symposium 2006

  22. Overview • Introduction to SWS • WSMO • Introduction to SOA • WSMX • Means of Interoperability • WSMT • Conclusions OASIS Symposium 2006

  23. Web Service Modeling Ontology (WSMO) • A conceptual model for Semantic Web Services: • Ontology of core elements for Semantic Web Services • a formal description language (WSML) • execution environment (WSMX) • … derived from and based on the Web Service Modeling Framework WSMF • an European Semantic System Initiative • “ESSI Cluster” Working Group • joint European research and development initiative OASIS Symposium 2006

  24. WSMO Working Groups A Conceptual Model for SWS A Formal Language for WSMO Execution Environment for WSMO A Rule-based Language for SWS OASIS Symposium 2006

  25. WSMO Design Principles Web Compliance Ontology-Based Strict DecouplingOf Modeling Elements Ontological Role Separation WSMO Centrality of Mediation Execution Semantics Description versus Implementation OASIS Symposium 2006

  26. WSMO Top Level Notions Objectives that a client wants to achieve by using Web Services Provide the formally specified terminology of the information used by all other components Semantic description of Web Services: • Capability (functional) • Interfaces (usage) Connectors between components with mediation facilities for handling heterogeneities OASIS Symposium 2006

  27. Non-Functional Properties Every WSMO elements is described by properties that contain relevant, non-functional aspects • Dublin Core Metadata Set: • complete item description • used for resource management • Versioning Information • evolution support • Quality of Service Information • availability, stability • Other • Owner, financial OASIS Symposium 2006

  28. Non-Functional Properties List Dublin Core Metadata Contributor Coverage Creator Description Format Identifier Language Publisher Relation Rights Source Subject Title Type Quality of Service Accuracy NetworkRelatedQoS Performance Reliability Robustness Scalability Security Transactional Trust Other Financial Owner TypeOfMatch Version OASIS Symposium 2006

  29. WSMO Ontologies Objectives that a client wants to achieve by using Web Services Provide the formally specified terminology of the information used by all other components Semantic description of Web Services: • Capability (functional) • Interfaces (usage) Connectors between components with mediation facilities for handling heterogeneities OASIS Symposium 2006

  30. Ontology Usage & Principles • Ontologies are used as the ‘data model’ throughout WSMO • all WSMO element descriptions rely on ontologies • all data interchanged in Web Service usage are ontologies • Semantic information processing & ontology reasoning • WSMO Ontology Language WSML • conceptual syntax for describing WSMO elements • logical language for axiomatic expressions (WSML Layering) • WSMO Ontology Design • Modularization: import / re-using ontologies, modular approach for ontology design • De-Coupling: heterogeneity handled by OO Mediators OASIS Symposium 2006

  31. Ontology Specification • Non functional properties (see before) • Imported Ontologiesimporting existing ontologies where no heterogeneities arise • Used mediators OO Mediators (ontology import with terminology mismatch handling) • Ontology Elements: Conceptsset of concepts that belong to the ontology, incl. Attributesset of attributes that belong to a concept Relationsdefine interrelations between several concepts Functionsspecial type of relation (unary range = return value) Instancesset of instances that belong to the represented ontology Axioms axiomatic expressions in ontology (logical statement) OASIS Symposium 2006

  32. WSMO Web services Objectives that a client wants to achieve by using Web Services Provide the formally specified terminology of the information used by all other components Semantic description of Web Services: • Capability (functional) • Interfaces (usage) Connectors between components with mediation facilities for handling heterogeneities OASIS Symposium 2006

  33. WS WS WS WSMO Web service description • complete item description • quality aspects • Web Service Management • Advertising of Web Service • Support for WS Discovery Capability functional description Non-functional Properties DC + QoS + Version + financial • realization of functionality by aggregating • other Web Services • functional • decomposition • WS composition • client-service interaction interface for consuming WS • External Visible • Behavior • - Communication • Structure • - ‘Grounding’ Web service Implementation (not of interest in Web Service Description) Choreography--- Service Interfaces --- Orchestration OASIS Symposium 2006

  34. Capability Specification • Non functional properties • Imported Ontologies • Used mediators • OO Mediator: importing ontologies with mismatch resolution • WG Mediator: link to a Goal wherefore service is not usable a priori • Pre-conditions • What a web service expects in order to be able to provide its service • Define conditions over the input. • Assumptions • Conditions on the state of the world that has to hold before the Web Service can be executed • Post-conditions • Describes the result of the WS in relation to the input, and conditions on it • Effects • Conditions on the state of the world that hold after execution of the • Web Service (i.e. changes in the state of the world) OASIS Symposium 2006

  35. Choreography & Orchestration VTA example: • Choreography = how to interact with the service to consume its functionality • Orchestration = how service functionality is achieved by aggregating other Web services When the service is requested When the service requests Hotel Service Date, Time Date VTA Service Hotel Time Error Flight, Hotel Confirmation Date, Time Error Flight Service Flight Confirmation Error Confirmation OASIS Symposium 2006

  36. Choreography Aspects • Interface for consuming Web Service • External Visible Behavior • those aspects of the workflow of a Web Service where Interaction is required • described by workflow constructs: sequence, split, loop, parallel • Communication Structure • messages sent and received • their order (communicative behavior for service consumption) • choreography related errors (e.g. input wrong, message timeout, etc.) • Grounding • concrete communication technology for interaction • Formal Model • reasoning on Web Service interfaces (service interoperability) • allow mediation support on Web Service interfaces OASIS Symposium 2006

  37. WS WS State in Orchestration Control Flow Data Flow Service Interaction Orchestration Aspects Control Structure for aggregation of other Web Services 1 Web Service Business Logic 3 2 • decomposition of service functionality • all service interaction via choreographies 4 OASIS Symposium 2006

  38. Orchestration Aspects • Service interfaces are concerned with service consumption and interaction • Choreography and Orchestration as sub-concepts of Service Interface • Common requirements for service interface description: • represent the dynamics of information interchange during service consumption and interaction • support ontologies as the underlying data model • appropriate communication technology for information interchange • sound formal model / semantics of service interface specifications in order to allow operations on them. OASIS Symposium 2006

  39. Choreography and Orchestration - Overview Choreography: - interaction of services / service and client - a „choreography interface“ describes the behavior of a Web Service for client-service interaction for consuming the service Orchestration: - how the functionality of a Web Service is achieved by aggregating other Web Services - extends Choreography descriptions by control & data flow constructs between orchestrating WS and orchestrated WSs. Conceptual models User language - based on UML2 activity diagrams - graphical Tool for Editing & Browsing Service Interface Description workflow constructs as basis for describing service interfaces: - workflow based process models for describing behavior - on basis of generic workflow constructs (e.g. van der Aalst) Formal description of service interfaces: - ASM-based approach - allows reasoning & mediation Grounding: - making service interfaces executable - currently grounding to WSDL Ontologies as data model: - every resource description based on ontologies - every data element interchanged is ontology instance OASIS Symposium 2006

  40. WSMO Goals Objectives that a client wants to achieve by using Web Services Provide the formally specified terminology of the information used by all other components Semantic description of Web Services: • Capability (functional) • Interfaces (usage) Connectors between components with mediation facilities for handling heterogeneities OASIS Symposium 2006

  41. Goals • Ontological De-coupling of Requester and Provider • Goal-driven Approach • derived from AI rational agent approach • Requester formulates objective independently • ‘Intelligent’ mechanisms detect suitable services for solving the Goal • allows re-use of Services for different purposes • Usage of Goals within Semantic Web Services • A Requester, that is an agent (human or machine), defines a Goal to be resolved • Web Service Discovery detects suitable Web Services for solving the Goal automatically • Goal Resolution Management is realized in implementations OASIS Symposium 2006

  42. Goal Specification • Non functional properties • Imported Ontologies • Used mediators • OO Mediators: importing ontologies with heterogeneity resolution • GG Mediator: • Goal definition by reusing an already existing goal • allows definition of Goal Ontologies • Requested Capability • describes service functionality expected to resolve the objective • defined as capability description from the requester perspective • Requested Interface • describes communication behaviour supported by the requester for consuming a Web Service (Choreography) • Restrictions / preferences on orchestrations of acceptable Web Services OASIS Symposium 2006

  43. WSMO Mediators Objectives that a client wants to achieve by using Web Services Provide the formally specified terminology of the information used by all other components Semantic description of Web Services: • Capability (functional) • Interfaces (usage) Connectors between components with mediation facilities for handling heterogeneities OASIS Symposium 2006

  44. Mediation • Heterogeneity … • Mismatches on structural / semantic / conceptual / functional / level • Occur between different components that shall interoperate • Especially in distributed & open environments like the Internet • Concept of Mediation (Wiederhold, 94): • Mediators as components that resolve mismatches • Declarative Approach: • Semantic description of resources • ‘Intelligent’ mechanisms that resolve mismatches independent of content • Mediation cannot be fully automated (integration decision) • Levels of Mediation within Semantic Web Services (WSMF): • Data Level: mediate heterogeneous Data Sources • Functional Level: mediate mismatches between Web Service/Goal and Web Service/Goals functionalities • Process/Protocol Level: mediate heterogeneous Business Processes/Communication Patterns • Layers of Mediators • Specification Layer – WSMO Mediators • Implementation Layer – Levels of Mediation OASIS Symposium 2006

  45. WSMO Mediators Overview OASIS Symposium 2006

  46. Mediator Structure Source Component WSMO Mediator uses a Mediation Service via 1 Target Component 1 .. n Source Component • as a Goal • directly • optionally incl. Mediation Specification layer Implementation layer Mediation Services OASIS Symposium 2006

  47. Goal: “merge s1, s2 and s1.ticket subclassof s2.product” OO Mediator - Example Merging 2 ontologies OO Mediator Mediation Service Train Connection Ontology (s1) Train Ticket Purchase Ontology Purchase Ontology (s2) Discovery Mediation Services OASIS Symposium 2006

  48. Aim: Support specification of Goals by re-using existing Goals Allow definition of Goal Ontologies (collection of pre-defined Goals) Terminology mismatches handled by OO Mediators Example: Goal Refinement GG Mediators GG Mediator Mediation Service Target Goal “Buy a Train Ticket” Source Goal “Buy a ticket” postcondition: “aTicket memberof trainticket” OASIS Symposium 2006

  49. WG & WW Mediators • WG Mediators: • link a Web Service to a Goal and resolve occurring mismatches • match Web Service and Goals that do not match a priori • handle terminology mismatches between Web Services and Goals • broader range of Goals solvable by a Web Service • WW Mediators: • enable interoperability of heterogeneous Web Services • support automated collaboration between Web Services • OO Mediators for terminology import with data level mediation • Protocol Mediation for establishing valid multi-party collaborations • Process Mediation for making Business Processes interoperable OASIS Symposium 2006

  50. Data Level Mediation • Scope • Solving terminological mismatches • Related Aspects / Techniques: • Ontology Integration (Mapping, Merging, Alignment) • Data Lifting & Lowering • Transformation between Languages / Formalisms • Terminology Mismatches Classification • Conceptualization Mismatches • same domain concepts, but different conceptualization • different levels of abstraction • different ontological structure • => resolution only includs human intervention • Explication Mismatches • mismatches between: • T (Term used), D (definition of concepts), C (real world concept) • => automated resolution partially possible OASIS Symposium 2006